1. Field of the Invention
The present invention relates to a scroll-type compressor (referred to as "scroll compressor" hereinafter) which is used as an air compressor or as a refrigerant compressor in a refrigeration or air-conditioning system. More specifically, the present invention is concerned with a scroll compressor having scroll wraps on both sides of an end plate and, hence, suitable to be realized as a large-size scroll-type compressor.
2. Description of the Related Art
In a conventional method for assembling a scroll-type fluid machine, the setting of the position of a stationary scroll member and an orbiting scroll member is conducted by bringing these scroll members into meshing engagement with each other, revolving the orbiting scroll while measuring the driving torque, and fixing the stationary scroll at a position where the torque is minimal, as in the case of an oil-less type scroll fluid machine disclosed in Japanese Utility Model Unexamined Publication No. 197086.
An air-cooled oil-less type scroll compressor disclosed in Japanese Utility Model Unexamined Publication No. 63136281 is of a single type which has a scroll wrap formed on only one side of the end plate of an orbiting scroll member. This type of scroll compressor, when required to have a large capacity, has to have a large diameter of scroll members. Increasing the diameter of the scroll members correspondingly increases the axial thrust load acted on the scroll members, which makes it difficult to design and control the compressor as a product. This type of scroll compressor, therefore, could be put to commercial production only when the capacity is as small as 5.5 Kw or less.
To overcome this disadvantage, scroll compressors of the type generally referred to as a "double scroll compressor" have been known in which scroll wraps defining compression chambers are provided on both sides of an end plate of an orbiting scroll member. Scroll compressors of this type can have a capacity exceeding 5.5 Kw, thus obviating the above-described problem. This type of scroll compressor is disclosed, for example, in Japanese patent Unexamined Publication No. 5776202 and Japanese Utility Model Unexamined Publication No. 587285. Thus, a double scroll compressor has scroll wraps on both sides of the end plate of an orbiting scroll member, in order to provide a large capacity. This type of scroll compressor, therefore, essentially incorporates a pair of stationary scroll members having wraps which mesh with both scroll wraps on the orbiting scroll member. It is to be noted that the setting of the positions of the pair of stationary scroll members and setting of the position of the orbiting scroll member cannot be done with high accuracy by the aforementioned method relying upon measurement of minimal torque. This is because the determination of scroll member positions relying upon measurement of the minimal torque is difficult to conduct due to the fact that the position setting which minimizes the torque acting between the orbiting scroll member and one of the stationary scroll members does not coincide with the position setting which minimizes the torque between the orbiting scroll member and the other scroll member.
Another problem encountered with oil-less scroll compressors, in particular air compressors, is that a suitable cooling measure has to be taken in view of the high temperature of the compressed gas, i.e., air, which well reaches 200.degree. C. or so. Namely, an oil-less scroll compressor in operation exhibits a high temperature of 200.degree. C. or so, since no lubricating oil which would serve as a coolant is introduced into the compression chamber of the compressor of this type. Such a high temperature tends to cause thermal distortion of both the orbiting and stationary scroll members, resulting in an increase in the gap between the meshing wraps or mutual contact between these wraps so as to make the rotational operation impossible. Consequently, the compression efficiency is impaired and, in the worst case, the compressor cannot operate at all.